Though the brunt of Hurricane Maria has left Puerto Rico, the island's water worries continue. On Friday afternoon, the National Weather Service reported that the Guajataca Dam in the northwest is "failing," causing flash flooding. Buses were trying to evacuate people from the area "as quickly as they can," the service said.

Officials say between 50,000 and 70,000 residents may have to be evacuated, according to the Associated Press, which also notes that authorities sent "frantic warnings on Twitter that went unseen by many in the blacked-out coastal area."

The dam failure is causing flooding downstream on the Guajataca River.

A flash flood watch is also in effect for much of the island through Friday evening with continued rainfall.

At least seven rivers in Puerto Rico are still running above "flood stage" (the point at which overflow begins to cause damage from flooding):

As Hurricane Maria passed, the entire main island saw persistent and intense rain that accumulated quickly. Caguas, about an hour inland from San Juan, saw 37.9 inches of rainfall, and most of the island got around 20 inches.

Los Angeles Times reporter Molly Hennessy-Fiske described the rain in San Juan as "white sheets of rain almost like a snowstorm. It's that intense and can get sort of whiteout effects."

Occasionally heavy rain is expected to continue until Tuesday, according to the NWS.